1. Field
A magnetic sensing element including a laminate and a bias layer is provided. The magnetic sensing element having a smaller variation in height between the top face of the laminate and top faces of regions where bias layers are disposed. The bias layers are disposed at both sides of the laminate in the track width direction, and the magnetic sensing element has a smaller variation in the distance between shield layers. Also provided is a process for producing the magnetic sensing element.
2. Description of the Related Art
FIGS. 10 to 15 show a process for producing a known tunneling magnetic sensing element. Each of Figures is a cross-sectional view in the production process of the tunneling magnetic sensing element taken along a plane parallel to a face facing a recording medium (the plane parallel to the X-Z plane).
As shown in FIG. 10, a laminate 7 is formed on a bottom shield layer 1, the laminate 7 including, an antiferromagnetic layer 2, a pinned magnetic layer 3, a nonmagnetic material layer 4, a free magnetic layer 5, and protective layer 6, formed in that order. The layers constituting the laminate 7 are formed on the entire surface of the bottom shield layer 1 by sputtering or the like. The protective layer 6 is composed of, for example, tantalum (Ta).
FIG. 11 shows a step of forming a resist layer 8 on the laminate 7. A resist is applied on the entire top face of the laminate 7 and is then subjected to exposure and development to form the resist layer 8 shown in FIG. 11. Portions of the laminate 7 not covered with the resist layer 8 are etched by ion milling to form the laminate 7 having a shape shown in FIG. 12 on the bottom shield layer 1.
As shown in FIG. 13, an underlying insulating layer 9 is formed over the top faces 1a of the bottom shield layer 1 at the both sides of the laminate 7 in the track width direction (X direction shown in the figure), both side end faces 7a and 7a of the laminate 7 in the track width direction (X direction), both side end faces 8a and 8a of the resist layer 8 in the track width direction (X direction), and the top face 8b of the resist layer 8. A hard bias layer 10 is formed on the underlying insulating layer 9. A milling stop layer 11 resistant to ion milling is formed on the hard bias layer 10. Here, the underlying insulating layer 9, the hard bias layer 10, and the milling stop layer 11 are also formed on the front end face (face facing toward the direction opposite to the Y direction) and rear end face (face facing toward the Y direction) of the resist layer 8. That is, the underlying insulating layer 9, the hard bias layer 10, and the milling stop layer 11 that each have a small thickness are disposed on the entire surface of the resist layer 8, except for the bottom face of the resist layer 8.
FIG. 14 shows a step of removing the underlying insulating layer 9, the hard bias layer 10, and the milling stop layer 11 disposed on the surface (the side end faces 8a and 8a, the top face 8b, the front end face, and the rear end face) of the resist layer 8 by ion milling.
The milling stop layer 11 is composed of a material having a milling rate lower than those of materials constituting the hard bias layer 10 and the underlying insulating layer 9 in ion milling. For example, the milling stop layer 11 is composed of tantalum (Ta). Hereinafter, the milling stop layer 11 on the surface of the resist layer 8 is referred to as an “over-resist milling stop layer 11a”. The milling stop layer 11 on the hard bias layer 10 disposed at each side of the laminate 7 in the track width direction (X direction) is referred to as an “on-bias milling stop layer 11b”. 
As shown in FIG. 14, the thickness H1 of the over-resist milling stop layer 11a disposed on the side end face 8a of the resist layer 8 is defined as a thickness in the direction parallel to the track width direction (X direction). The thickness H1 of the over-resist milling stop layer 11a is smaller than that of the on-bias milling stop layer 11b. The over-resist milling stop layer 11a can be successfully removed by adjusting a milling angle in ion milling. After the removal of the over-resist milling stop layer 11a by ion milling, the hard bias layer 10 and the underlying insulating layer 9 disposed on the side end face 8a and the like of the resist layer 8 are removed by ion milling. The underlying insulating layer 9, the hard bias layer 10, the over-resist milling stop layer 11a, and the on-bias milling stop layer 11b that have removed by ion milling are indicated by dotted lines.
As shown in FIG. 14, the on-bias milling stop layer 11b has been partially removed by ion milling. The on-bias milling stop layer 11b has a sufficient thickness so as not to be entirely removed in the ion-milling step. Thus, part of the on-bias milling stop layer 11b appropriately remains on the hard bias layer 10. Therefore, the remaining on-bias milling stop layer 11b can prevent the hard bias layer 10 under the on-bias milling stop layer 11b from being etched by ion milling.
The resist layer 8 that has been exposed by removing the hard bias layer 10 and the over-resist milling stop layer 11a is removed by dissolution with a dissolving solution, thereby resulting in the appearance of the top face 7b of the laminate 7, the top face 7b being identical to the top face of the protective layer 6. By performing the above-described steps, a tunneling magnetic sensing element is completed, the tunneling magnetic sensing element including the laminate 7 on the bottom shield layer 1, the hard bias layer 10 at each side of the laminate 7 in the track width direction (X direction), and the on-bias milling stop layer 11b on part of each hard bias layer 10.
FIG. 15 shows a step of forming a top shield layer 15 on the tunneling magnetic sensing element.
Japanese Unexamined Patent Application Publication Nos. 2004-335071 and 2005-44489 each disclose a current-perpendicular-to-plane-mode (CPP-mode) magnetic sensing element.
The tunneling magnetic sensing element produced by the above-described steps disadvantageously includes a large step height between the top face 7b of the laminate 7 and the top face 11b1 of the on-bias milling stop layer 11b disposed (remaining) at each side of the laminate 7 in the track width direction (X direction). As shown in FIG. 15, the top faces 11b1 of the on-bias milling stop layers 11b are disposed at positions lower than that of the top face 7b of the laminate 7. This is because the on-bias milling stop layers 11b are partially etched by ion milling in the ion milling step shown in FIG. 14.
Each underlying insulating layer 9 and each hard bias layer 10 have milling rates significantly higher than those of the on-bias milling stop layers 11b in ion milling and are disposed between the laminate 7 and the corresponding on-bias milling stop layer 11b. The underlying insulating layers 9 and the hard bias layers 10 disposed here are not covered with the on-bias milling stop layers 11b. The top face A of each uncovered underlying insulating layer 9 and each uncovered hard bias layer 10 between the laminate 7 and the corresponding on-bias milling stop layer 11b is etched by ion milling at a high etch rate. Consequently, the position of each top face A is lower than that of the top face 11b1 of each on-bias milling stop layer 11b, thus resulting in a very high step height between the corresponding top face A and the top face 7b of the laminate 7. Furthermore, an area ranging from each top face A to the top face 11b1 of the corresponding on-bias milling stop layer 11b has a curved surface.
In the tunneling magnetic sensing element produced by such a known production process, for example, a distance H2 is defined as a distance between the bottom shield layer 1 and the top shield layer 15 at a region where the laminate 7 is disposed, and a distance H3 is defined as a distance between the bottom shield layer 1 and the top shield layer 15 at each side of the laminate 7 in the track width direction (X direction). Comparison of the distance H2 with the distance H3 shows a large difference. Furthermore, there is a large variation in the distance between the bottom shield layer 1 and the top shield layer 15 at each side of the laminate 7 in the track width direction (X direction) because the position of the top face in the vicinity of the laminate 7 is significantly lower than that of the top face 7b of the laminate 7.
If the film-forming angle and the like are adjusted in such a way that the underlying insulating layer 9, the hard bias layer 10, and the milling stop layer 11 are not formed on the surface of the resist layer 8 unlike FIG. 13 when the underlying insulating layer 9, the hard bias layer 10, and the milling stop layer 11 are formed, the ion milling step shown in FIG. 14 is not required, thus not leading to the above-described problems. However, if the above-described adjustment is performed, the thick hard bias layer 10 and the like cannot be formed at each side of the laminate 7 in the track width direction (X direction) because of a shadow effect of the very thick resist layer 8. Furthermore, when the unnecessary laminate 7 shown in FIG. 12 is removed by ion milling, part of a material constituting the laminate 7 is deposited on the surface of the resist layer 8 (redeposition problem). After all, it was found that an ion milling step of removing the redeposit is required. Thus, the known process for producing the tunneling magnetic sensing element was not able to reduce the variation in the distance between the shield layers.